An intensity modulating system and a phase modulating system are well known as two modulating systems in the optical communications. Two well known phase modulating systems are a method of performing a modulation by interference of a signal itself and a method of performing a modulation by interference of local light and a signal. The method of interference by a signal itself can be, for example, DPSK (differential phase shift keying) for performing a binary modulation and DQPSK (differential quadrature phase shift keying) for performing a quarternary modulation. The method of interference by local light and a signal can be DP-QPSK (dual polarization-quadrature phase shift keying) etc. for performing an octal modulation.
Conventionally, the following technique is well known as a wire bonding method for a semiconductor chip. Described is a semiconductor device in a multichip system storing a plurality of semiconductor chips in which a bonding pad is provided near one side of a second semiconductor chip loaded into a first semiconductor chip, and the bonding pad of the semiconductor chips is connected directly by a wire. Thus, the number of bonding pads of the substrate mounted with the semiconductor chips can be reduced, thereby realizing a small package (for example, cited document 1).
Described is an integrated circuit chip in which an output pad connected by a wire is arranged at a position other than the periphery of the upper surface. Along two edges on the upper surface of the integrated circuit chip, a wire bonding adapter having a bonding pad is arranged. The output pad at the center of the integrated circuit chip is connected to the bonding pad of one edge of the wire bonding adapter through a wire. Next, the bonding pad of another edge of the wire bonding adapter is connected to the pad of the substrate through the wire. Thus, even when an integrated circuit chip is laid on another integrated circuit chip, the wire bonding can be performed (for example, cited document 2).
In addition, described is a semiconductor integrated circuit device in which a built-in semiconductor chip is connected to a lead through wire bonding. In the device, a semiconductor chip is mounted at a wiring plate having a signal line for changing the connection path of the connecting pad of the semiconductor chip. Thus, any connecting pad of the semiconductor chip can be connected to any lead (for example, patent document 3).
A method of transmitting a signal at a high speed in the photoreceiving device for receiving an optical signal can be a method of performing the binary modulation using a high-speed optical element and a high-speed amplifier, and a method of performing a multivalued modulation using a low-speed optical element and a low-speed amplifier.
FIG. 1 is a schematic diagram of the structure of a photoreceiving device 10. A base member 11 is provided with a photoreceiving element 12 and an amplifier 13 for amplifying an output signal of the element. The photoreceiving device 10 is stored in a case, and power supply terminals 14 and 15 are provided at the left and right sides (as viewed from the front in FIG. 1) of the case.
The photoreceiving element 12 receives light from the front in FIG. 1 as indicated by the arrow in FIG. 1, and after an optical signal is converted into an electric signal, it is output backward after amplifying by the amplifier 13.
A plurality of terminals for connecting a power supply are provided for both sides of the amplifier 13. These power supply terminals are connected to power supply terminals 14 and 15 connected to an external power supply through a wire. In this case, since the power supply terminals 14 and 15 are provided for the left and right sides of the case, each wire can be connected to the power supply terminals 14 and 15 from the terminals at both sides of the amplifier 13.
FIG. 2 is a schematic diagram of the structure of a photoreceiving device 21 in which two photoreceiving devices 10a and 10b are stored in one case.
The photoreceiving device 10a includes a photoreceiving element 12a and an amplifier 13a. After the signal amplified by the amplifier 13a is output to a high frequency substrate 16, it is output to an external terminal not illustrated in the attached drawings.
The photoreceiving device 10b also includes a photoreceiving element 12b and an amplifier 13b. After the signal amplified by the amplifier 13b is output to a high frequency substrate 17, it is output to an external terminal not illustrated in the attached drawings.
Terminals for connecting a power supply are provided at both sides of the 13ab. Therefore, it is necessary to arrange the wires for connecting the terminal for connection of the power supply at the left side of the amplifier 13a to the power supply terminal 14 across the area above the amplifier 13a. Similarly, it is necessary to arrange the wires for connecting the terminal for connection of the power supply at the right side of the amplifier 13b to the power supply terminal 15 across the area above the amplifier 13b. 
If the above-mentioned wiring arrangement is performed, the length of the wiring is long, and the inductance of the power supply line increases. The internal noise generated by an amplifier is the noise having nearly equal frequency to the main signal (for example, a signal of a frequency of 40 Gbps or more). When the inductance of the power supply line becomes high, the internal noise is reflected and returns to the amplifier and affects the main signal. Therefore, it is preferable that the wire is short.
Furthermore, when the wiring arrangement concentrates at one side of the amplifier 13, the distance between wires becomes short, and the stray capacitances become large, thereby causing the problem of crosstalk.